Amazon makes it easy for Kindle users to download their notes and highlights, but we can't say the same for Kobo, which obscures a user's notes in a database file.
You'll need to set up an account, and then upload the "KoboReader.sqlite" file from your Kobo ereader, and once you do you will be able to sort the notes by the book they cam from.
The site displays the notes onscreen one book at a time, with all of a book's notes listed on a single page. As you can see, there's no way to distinguish between a highlight (text copied from the book) form an annotation (a user's own note):
KoboNotes.com is, to the best of my knowledge, the only tool which lets you extract note from a Kobo ereader (I can't find a way to do this with calibre, in case you were wondering).
This is a useful site, but it's not without its issues. One commenter pointed out on MR that this site represents a serious security concern:
Really? You want me to load a file that has a list of every book I have on the device to your web site? And includes the key information that Kobo uses to validate my device every time it calls home? Sorry, as useful as this might be, it's not going to happen.
They're right; this is a sound reason to avoid using the site if you read sensitive documents or have concerns about your security or privacy.
image by andsleonardo